Reflective crops contribute to climate change mitigation

Albedo change can make an important contribution to the climate impact of cropping systems. Albedo is the share of solar radiation reflected back from the ground. It ranges between 5 and 30% for bare and vegetated agricultural land, and can reach up to 90% due to snow cover. The more reflective a surface, the higher its albedo and the greater the potential for radiative cooling and eventually temperature change.

Photograph by Sergio Lorenc

Albedo has increased globally due to agricultural expansion, converting forests to more reflective grass- and croplands. However, deforestation is associated with losses of crucial ecosystem functions including carbon storage and local surface cooling by evapotranspiration. Managing agricultural land to achieve higher reflectivity has the potential to mitigate local heat waves and global warming. Strategies to increase the albedo of croplands include selection of reflective species or varieties, introduction of cover crops, intercropping, residue retention, and delayed or no ploughing.

In a recently published article, we studied how cultivating abandoned land with short-rotation willow affects albedo and evaluated its potential as a climate change mitigation measure. We found that albedo increased from 16.5 to 21.5% on average when fallow land was cultivated with willow, based on three years of field-measured data. These data were subsequently combined with a time-dependent life cycle assessment (LCA) model of bioenergy produced from willow. Here, we included emissions from the production of inputs, field operations, soil, transport and energy conversion.

Simulating processes and emission along the life cycle and impacts on climate over time allowed us to compare the effect of albedo change (cooling) to that of greenhouse gas emissions (warming) and carbon sequestration in biomass and soil (cooling). In sum, the bioenergy system had a net cooling effect because albedo change and carbon sequestration outweighed emissions from the supply chain and soil. Our results over time showcase the different nature of albedo and long-lived greenhouse gases as climate forcers. Albedo change needs to be sustained for years in order to offset the temperature response to a one-off greenhouse gas emission.

The article has been published open access in GCB Bioenergy:
Sieber, P., Ericsson, N., Hammar, T., & Hansson, P.-A. Including albedo in time-dependent LCA of bioenergy. GCB Bioenergy, n/a(n/a). doi:10.1111/gcbb.12682

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